This application claims priority of Korean Application Nos. 2001-63808, filed on Oct. 16, 2001 and 2002-788 filed on Jan. 7, 2002 in the Korean Patent Office, the entire contents of which are incorporated herein by reference.
The present invention relates to a cathode ray tube, and more particularly, to a cathode ray tube that uses a degaussing coil for demagnetizing metal parts in the cathode ray tube such as a color selection apparatus and an inner shield.
Metal parts such as a color selection apparatus and an inner shield are typically found in a cathode ray tube (CRT). The color selection apparatus includes a shadow mask that has a plurality of apertures for performing color separation of three electron beams, which are emitted from an electron gun to corresponding R, G, B phosphors of a phosphor screen, and a mask frame for fixedly supporting the shadow mask at a predetermined location in the CRT. The inner shield performs the function of shielding a path through which the electron beams travel from the earth""s magnetic field.
However, the metal parts nevertheless become magnetized by the earth""s magnetic field such that a magnetic field is formed in the peripheries of the metal parts. Such a magnetic field changes the paths through which the electron beams travel such that the intended phosphors are not illuminated by the electron beams. That is, mis-landing of the electrons beams occurs, which reduces picture quality.
To remedy this problem, a degaussing coil is mounted on an outer circumference of a funnel of the CRT. The degaussing coil operates for a period of three or four seconds each time the CRT is turned on to demagnetize the color selection apparatus and the inner shield using a demagnetization current.
Japanese Laid-open Patent Nos. Heisei 5-260496, Heisei 5-283019, and Heisei 6-62419 disclose CRTs, in which a pair of degaussing coils is mounted in approximately an M-shape on an outer circumference of a funnel of the CRT. However, when designing the shape and mounting position of the degaussing coils in these conventional CRTs, the formation and positioning of the metal parts (e.g., shadow mask and mask frame) within the CRT, and of an explosion proof band and ears that are mounted toward a panel of the CRT are generally first considered. However, no sufficient consideration is given to the relation with the inner shield, which plays a major part in determining the path of the electron beams.
Japanese Laid-open Patent No. Heisei 10-210491 discloses a CRT, in which a degaussing coil is mounted closer to a front face of a panel than are ears of the CRT. However, when using the CRT with such a configuration in an actual television, computer monitor, etc., the degaussing coil becomes a hindrance when mounting the CRT in an assembly that houses the same, such as a television cabinet. As a result, productivity is reduced during manufacturing of the assembly that houses such CRT.
In accordance with the present invention a cathode ray tube is provided which uses a degaussing coil capable of sufficiently demagnetizing a color selection apparatus, as well as an inner shield.
Also, in accordance with the present invention, a cathode ray tube is provided which uses a degaussing coil, in which the degaussing coil does not interfere with the mounting of the cathode ray tube in a housing during manufacturing, thereby improving productivity.
In one embodiment, the present invention provides a cathode ray tube including a panel, a funnel, and a neck. The cathode ray tube also includes a color selection apparatus mounted to the panel within the tube; a inner shield connected to the color selection apparatus and including a plurality of side walls that form a center opening through which electron beams pass; at least one degaussing coil mounted an outer surface of the tube. The degaussing coil includes a first coil mounted toward the panel; a second coil mounted toward the neck; and a third coil connected to ends of the first coil and the second coil to interconnect the first coil and the second coil. The second coils is mounted on the tube in a state substantially overlapping distal edge portions of the side walls of the inner shield on which the second coils are mounted.
If a length of the distal edge portions of the side walls of the inner shield on which the second coil is mounted is L1, and a length of the second coils is L2, the following condition is satisfied:
L1xe2x89xa6L2. 
If a distance between the distal edge portions of the side walls of the inner shield on which the second coils are mounted is D1, and a distance between second coils is D2, the following condition is satisfied:
0.7xe2x89xa6(D2/D1)xe2x89xa61.3. 
The distances D1 and D2 are minimal lengths.
The second coil is are formed along substantially identical horizontal lines as the distal edge portions on which the second coils are mounted.
In one embodiment, the color selection apparatus includes a mask frame including two pairs of support members, the support members of each pair are at a predetermined distance from each other, and a pair of elastic members, each of which extends to interconnect the support members comprising each pair of the same; and a mask having a plurality of apertures, the support members of the mask frame being connected to the mask, and the mask being mounted receiving tension in a direction corresponding to a width of the panel.
An explosion proof band having a plurality of ears is mounted on the skirt of the panel, and the first coils are mounted on the explosion proof band in a state positioned farther from a front face of the panel than the ears.
In another embodiment, an explosion proof band having a plurality of ears is mounted on the skirt of the panel, and the first coils include first sub coils mounted on the skirt at a position farther from a front face of the panel than the explosion proof band; second sub coils mounted on the explosion proof band at a position closer to the front face of the panel than the ears; and third sub coils interconnecting the first sub coils and the second sub coils.
The first coils further include fourth sub coils mounted on the explosion proof band at a position farther from the front face of the panel than the ears; and fifth sub coils interconnecting the fourth sub coils and the first sub coils.